Method of manufacturing wave-guides of the kind having a vacuum-tightly clamped-in mica window and waveguides manufactured by said methods



16, 1965 B. B. VAN IPEREN ETAL 3, 7,3

METHOD OF MANUFACTURING WAVE-GUIDES OF THE KIND HAVING A vACUUM-TIGHTLY CLAMPED-IN MICA WINDOW AND WAVEGUIDES MANUFACTURED BY SAID METHODS Filed Feb. 4. 1965 United States Patent 3 267 398 METHOD OF MANUE ACTURING WAVE-GUHDES OF THE KIND HAVING A VACUUlW-TIGHTLY CLAMPED-IN MICA WINDOW AND WAVE- GUIDES MANUFACTURED BY S METHODS Beruardus Bastiaan van Iperen, Wilhelmus Kuypers, and

Martiuus Cornelis Verhagen, all of Emmasingel, Eindhoven, Netherlands, assiguors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 4, 1965, Ser. No. 430,403 Claims priority, application Netherlands, Feb. 12, 1964, 6,401,186 3 Claims. (Cl. 333-98) The invention relates to a method of manufacturing a waveguide, particularly to a method of providing a vacuum-tight connection of an insulating window in such a waveguide, particularly for use at wavelengths of less than 3 mms.

In many cases such a waveguide is partly associated with the vacuum space of an electron tube connected thereto. The waveguide must then have an insulating window which provides a vacuum-tight closure but constitutes a minimum obstacle for the high-frequency currents. With wavelengths above 5 mms. satisfactory results are obtained by the known constructions in which the waveguide is provided with a groove in which an insulating plate is sealed in a vacuum-tight manner by means of glass or solder. However, the groove constitutes an irregularity in the waveguide, which involves gradually greater disadvantages for wavelengths further below 5 mms. There are known structures in which the two portions of the waveguide on either side of the insulating window are prolonged up to the surface of the window, the groove being thus bridged. However, these structures require very accurate machining of the portions of the waveguide, whilst the thickness of the insulating window must have small tolerances.

-It is furthermore known to clamp a mica plate between two ends of tubular portions of a waveguide, in which case one of these tubular portions may be of a plastic metal, the portions being fastened in a cylindrical envelope so that upon heating the ends of the portions are very heavily urged against the mica window owing to the expansion of said portions. Then the plastic metal establishes a vacuum-tight junction with the mica surface. The cylindrical envelope then serves for mechanical rigidity. Also this requires accurate machining and small tolerances, whilst the construction is complicated.

All said disadvantages can be eliminated by using the method according to the invention, when the ends of the two portions of the waveguide consisting at least partly of plastic metal are machined by a milling operation so as to be optically smooth and are arranged one on the other with the interposition of an insulating plate so that the insulating plate overlaps the aperture of the waveguide on all sides, whilst the outer edge of the insulating plate is located at a given distance inside the outer periphery of the ends of the waveguide portions, after which the ends of the waveguide are pressed together with such a high pressure and then heated that the insulating plate is embedded in the material of the portions, which portions are vacuumtightly connected together and to the surface of the insulating plate by diffusion.

It is found that particularly with wavelengths below 2 mms. the disturbance of the guidance of the waves through a window embedded in the metal of the waveguide in the manner described above is at a minimum, whilst small tolerances of the dimensions of the insulating plate and of the waveguide portions are not necessary.

It is known per se to join waveguide portions by means of diffusion, but in this case no vacuum-tight insulating Window was used.

The invention will be described more fully with reference to the drawing, the figure of which shows a sectional view of a window in a waveguide manufactured by the method according to the invention.

The portions 1 and 2 of a waveguide consisting for example of copper, portion 1 for example being connected with a vacuum space, are provided with flanges 2 and 4. These flanges are machined by milling operations so as to be optically smooth so that the unevennesses on the opposite surfaces 6 are smaller than 1,. Machining of the said surfaces to optional smoothness can be carried out by means of commercially available special lathes or milling machines. Grinding is not allowed, since the grinding paste penetrates into the surface and constitutes, subsequent to diffusion, a porous, non-vacuum-tight weld.

Then with the interposition of a mica window 5 the flanges are put one on the other, so that the smooth surfaces of the flanges 2 and 4 are spaced apart by a distance equal to the thickness of the plate 5.

In accordance with the invention such a pressure is exerted on the flanges 2 and 4, whilst the flanges are heated at about 475 C. to 500 C. for about one hour, that the copper of the flanges flows around the mica plate 5, the flanges thus coming into contact with each other, and the mica plate being embedded in the material of the flanges. It is found that subsequent to the heating process the material of the flanges forms a vacuum-tight seal at the junction 6 by diffusion, so that even after etching a transitional area can hardly be shown. It is furthermore found that the material of the portions 1 and 3 is sealed in a vacuumtight manner to the mica surface. The mica window has a thickness of for example i to 15 and it may have a diameter of for example 2 mm. Such Waveguides may also be manufactured very efiicaceously for wavelengths of less than 1 mm. The section may be circular, square or of any other shape. The dimensions of the mica window may have large tolerances, since the plate need not fit in correspondingly shaped grooves.

It will be obvious that apart from copper, other plastic metals such as silver, gold or aluminum may be employed as a material for the ends of the waveguide portions.

What is claimed is:

1. A method of manufacturing a waveguide in which an insulating window is vacuum-tightly clamped in between two portions of the waveguide, characterized in that the ends of the portions of the waveguide consisting at least partly of a plastic metal, are machined by a milling operation so as to be optically smooth and are arranged one on the other with the interposition of an insulating plate so that the insulating plate overlaps the aperture of the wave guide on all sides, whilst the outer edge of the insulating plate is located at a given distance inside the outer periphery of the ends of the waveguide portions, after which the waveguide ends are pressed together with such a high pressure that the insulating plate is embedded in their material whilst the waveguide portions are vacuum-tightly connected together and to the surface of the insulating plate by diffusion.

2. A waveguide, particularly for wavelengths of less than 2 mms. manufactured by the method claimed in claim 1, characterized in that the insulating window in embedded in the material of the waveguide portions which are interconnected beyond the Window by diffusion.

3. A waveguide as claimed in claim 2, characterized in that the window is made of mica having a thickness of 15 1. or less and the waveguide is made of copper.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner. L. ALLAHUT, Assistant Examiner. 

1. A METHOD OF MANUFACTURING A WAVEGUIDE IN WHICH AN INSUALTING WINDOW IS VACUUM-TIGHTLY CLAMPED IN BETWEEN TWO POSITIONS OF THE WAVEGUIDE, CHARACTERIZED IN THAT THE ENDS OF THE PORTIONS OF THE WAVEGUIDE CONSISTING AT LEAST PARTLY OF A PLASTIC METAL, ARE MACHINED BY A MILLING OPERATION SO AS TO BE OPTICALLY SMOOTH AND ARE ARRANGED ONE ON THE OTHER WITH THE INTERPOSITION OF AN INSULATING PLATE SO THAT THE INSULATING PLATE OVERLAPS THE APERTURE OF THE WAVEGUIDE ON ALL SIDES, WHILST THE OUTER EDGE OF THE INSULATING PLATE IS LOCATED AT A GIVEN DISTANCE INSIDE THE OUTER PERIPHERY OF THE ENDS OF THE WAVEGUIDE PORTIONS, AFTER WHICH THE WAVEGUIDE ENDS ARE PRESSED TOGETHER WITH SUCH A HIGH PRESSURE THAT THE INSULATING PLATE IS EMBEDDED IN THEIR MATERIAL WHILST THE WAVEGUIDE PORTIONS ARE VACUUM-TIGHTLY CONNECTED TOGETHER AND TO THE SURFACE OF THE INSULATING PLATE BY DIFFUSION. 